Vaccines protect chickens against H5 highly pathogenic avian influenza in the face of genetic changes in field viruses over multiple years
Introduction
Avian influenza (AI) occurs worldwide and is caused by Type A orthomyxoviruses of 15 haemagglutinin (H1–H15) and nine neuraminidase subtypes (Easterday et al., 1997). AI viruses can infect a diverse variety of bird species, including domestic poultry. With AI virus, there are two main pathotypes based upon infections of chickens and turkeys: (1) mildly pathogenic (MP) AI typically associated with respiratory disease, drops in egg production and/or mild to moderate increases in mortality and (2) highly pathogenic (HP) AI typically producing severe systemic disease, and high losses (Swayne et al., 1998, Perdue et al., 2000). In developed countries, AI viruses are not endemic in integrated commercial poultry systems, and control measures are taken to prevent introduction of AI or to eliminate AI if sporadic outbreaks occur of MP or HP AI.
Historically, individual nations have chosen control or eradication strategies to meet domestic needs and, to a lesser extent, requirements for international commerce of poultry and poultry products (Lancaster, 1981). Such strategies vary from tolerance of infections in poultry to a multi-faceted control program utilizing education of farmers and workers on avian influenza control, enhanced biosecurity on farms, increased surveillance and diagnostics, implementation of quarantine zones and controlled movement of birds within infected areas, and some method of eliminating infected birds (Lancaster, 1981). In addition, vaccines have been used in the US since the late 1970s for control of sporadic outbreaks of MP AI in turkeys (Lancaster, 1981). Recently, vaccines have been used in control programs for HP AI outbreaks in chickens in Mexico and Pakistan (Naeem and Hussain, 1995). In USA, the Animal and Plant Health Inspection Service has adopted a strategy for future control of HP AI that could potentially include vaccine use in emergency eradication program (Myers and Morgan, 1998).
By contrast, influenza is endemic in the human population and yearly vaccination is practised commonly throughout the developed nations (Murphy and Webster, 1996). An inactivated trivalent vaccine is central to the control and prevention of types A and B influenza, but because of antigenic drift of AI viruses in the field, the vaccines have a finite life span and the strain composition of the vaccine is changed on an annual basis (CDC, 1998).
The following studies were conducted to determine if H5 AI vaccines would need to be changed on a frequent basis in order to overcome antigenic changes in the field over time and maintain efficacy in chickens.
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Experiment 1: inactivated avian influenza virus vaccines
Groups of 10 4-week-old specific-pathogen-free (SPF) White Leghorn (WL) chickens obtained from flocks maintained at Southeast Poultry Research Laboratory were immunized subcutaneously with each of the 12 candidate inactivated vaccines prepared as described (Stone, 1987). Vaccines used included an uninoculated egg fluid (sham), a H7 AI virus and 10 H5 AI viruses (Table 1). Challenge was at 3 weeks post-vaccination (PV) by intranasal-(IN)-inoculation of 107.7 mean embryo lethal doses (ELD50) of
Experiment 1: inactivated avian influenza virus vaccines
The HA1 segment of the haemagglutinin protein from the H5 vaccine viruses had 91.9–100% deduced amino acid sequence similarity to the HA1 of the HP Q1/95 H5 challenge virus. The heterologous H7 AI vaccine had 35.9% similarity with the HA1 of the H5 challenge AI virus. The H5 vaccine and challenge AI viruses were of the North American lineage of H5 AI viruses.
For the H5 vaccine groups, most vaccinated chickens lacked clinical signs and survived challenge by a H5 HP Q1/95 AI virus (Table 1) while
Discussion
The inactivated whole AI virus vaccines, baculovirus-derived AI haemagglutinin vaccine and recombinant fowlpoxvirus-AI haemagglutinin vaccine protected chickens from clinical signs and death following lethal challenge by multiple HP H5 AI viruses. The vaccine and challenge viruses, or their haemagglutinin protein components, were from field AI viruses of diverse backgrounds and included strains obtained from four different continents (North America, Europe, Asia and Africa), six different host
Acknowledgements
The data were presented at the European Society of Veterinary Virology, Symposium on Influenza, Ghent, Belgium, 16–18 May 1999 and have been published in complete detail elsewhere (Crawford et al., 1999, Swayne et al., 1999, Swayne et al., 2000).
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Practical aspects of vaccination of poultry against avian influenza virus
2014, Veterinary JournalProtection against H7N3 high pathogenicity avian influenza in chickens immunized with a recombinant fowlpox and an inactivated avian influenza vaccines
2013, VaccineCitation Excerpt :According to clinical protection and prevention of virus shedding, serological data also suggested that protection from HPAIV was similar but not equal among immunized groups. Characterization of the pre- and post-challenge HI titers identified antibody responses that were cross-reactive among the three tested seed strains, thus suggesting a broad range of immunity after AI vaccination with vaccine seed strains of diverse antigenic relatedness, as previously described [13,18,19,23]. Indeed, the A/Turkey/Virginia/66/02 isolate and the A/Cinnamon Teal/Mexico/2817/2006 isolate had 93.7% amino acid similarity in HA to each other, and 94.0% and 97.9% similarity with the challenge virus Jalisco/12, respectively, when compared by CLUSTAL W analysis.
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Current Address: Department of Avian Medicine, The University of Georgia, 953 College Station Road, Athens, GA 30605, USA.